Why is cursor already closed ?

[AlwaysNoobCoder]

I am invoking mapper by reflection, and outer method was annotated by @transactional:

@Override
	@Transactional(readOnly = true)
	protected void handleTextMessage(WebSocketSession session, TextMessage message) {
		String locator = session.getUri().getPath().replace("/export/sea/", "");
		log.info("incoming SEA export request: {} {}", session.getUri().getPath(), locator);
		try {
			SEAReadRequest req = objectMapper.readValue(message.getPayload(), SEAReadRequest.class);
			req.setLocator(locator);
			handler.doStreamingRead(req, t -> {
				try {
					session.sendMessage(new TextMessage(t.toString()));
				} catch (IOException e) {
					e.printStackTrace();
				}
			});
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

public <T> void doStreamingRead(SEAReadRequest req, Consumer<T> consumer) throws Exception {
		ISEAMapper seaMapper = seaContext.getRegistry().getMapper(req.getLocator());
		if (seaMapper == null) {
			throw new Exception("unknown locater: " + req.getLocator());
		}
		String routine = ((MybatisSEAMapper) seaMapper).getReadMethod();
		String mapperBeanName = routine.split("#")[0];
		String readMethod = "streamByExample";
		String readCountMethod = routine.split("#").length >= 3 ? routine.split("#")[2] : null;
		Object mapperInstance = sqlSession.getMapper(Class.forName(mapperBeanName));
		Class<T> cls = (Class<T>) seaContext.getEntityType(req.getLocator());
		Class<?> mapperClass = mapperInstance.getClass();
		for (Method m : mapperClass.getMethods()) {
			if (m.getName().equals(readMethod) && m.getReturnType().getName().equals("org.apache.ibatis.cursor.Cursor")) {
				Class<?> exampleClass = m.getParameterTypes()[0];
				Object exampleInstance = exampleClass.getDeclaredConstructor().newInstance();
				Cursor<T> result;
				// selective query
				if (req.getIncludes() != null) {
					exampleClass.getMethod("setIncludes", LinkedHashSet.class).invoke(exampleInstance, req.getIncludes());
				}

				// filtering
				if (req.getFilter() != null) {
					exampleClass.getMethod("setFilter", Filter.class).invoke(exampleInstance, req.getFilter());
				}

				// sorting
				if (req.getSort() != null && !req.getSort().isEmpty()) {
					exampleClass.getMethod("setOrders", LinkedHashSet.class).invoke(exampleInstance, req.getSort());
				}
				
				result = (Cursor<T>) mapperClass.getMethod(readMethod, exampleClass).invoke(mapperInstance, exampleInstance);
				
				result.forEach(consumer);
			}
		}
	}

when doing this:

2024-04-12T10:25:04.133+08:00 DEBUG 12567 --- [nio-8080-exec-2] c.w.i.s.p.m.UserMapper.streamByExample   : ==> Parameters: 
java.lang.IllegalStateException: A Cursor is already closed.
	at org.apache.ibatis.cursor.defaults.DefaultCursor.iterator(DefaultCursor.java:100)
	at java.base/java.lang.Iterable.forEach(Iterable.java:74)
	at fwx.sea.impl.mybatis.MybatisSEARequestHandler.doStreamingRead(MybatisSEARequestHandler.java:228)
	at com.wxt.itps.services.pub.ws.SEAExportWSHandler.handleTextMessage(SEAExportWSHandler.java:49)
	at org.springframework.web.socket.handler.AbstractWebSocketHandler.handleMessage(AbstractWebSocketHandler.java:43)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:351)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:713)
	at com.wxt.itps.services.pub.ws.SEAExportWSHandler$$SpringCGLIB$$0.handleMessage(<generated>)
	at org.springframework.web.socket.handler.WebSocketHandlerDecorator.handleMessage(WebSocketHandlerDecorator.java:75)
	at org.springframework.web.socket.handler.LoggingWebSocketHandlerDecorator.handleMessage(LoggingWebSocketHandlerDecorator.java:56)
	at org.springframework.web.socket.handler.ExceptionWebSocketHandlerDecorator.handleMessage(ExceptionWebSocketHandlerDecorator.java:58)
	at org.springframework.web.socket.adapter.standard.StandardWebSocketHandlerAdapter.handleTextMessage(StandardWebSocketHandlerAdapter.java:113)
	at org.springframework.web.socket.adapter.standard.StandardWebSocketHandlerAdapter$1.onMessage(StandardWebSocketHandlerAdapter.java:70)
	at org.springframework.web.socket.adapter.standard.StandardWebSocketHandlerAdapter$1.onMessage(StandardWebSocketHandlerAdapter.java:67)
	at org.apache.tomcat.websocket.WsFrameBase.sendMessageText(WsFrameBase.java:387)
	at org.apache.tomcat.websocket.server.WsFrameServer.sendMessageText(WsFrameServer.java:130)
	at org.apache.tomcat.websocket.WsFrameBase.processDataText(WsFrameBase.java:484)
	at org.apache.tomcat.websocket.WsFrameBase.processData(WsFrameBase.java:284)
	at org.apache.tomcat.websocket.WsFrameBase.processInputBuffer(WsFrameBase.java:130)
	at org.apache.tomcat.websocket.server.WsFrameServer.onDataAvailable(WsFrameServer.java:85)
	at org.apache.tomcat.websocket.server.WsFrameServer.doOnDataAvailable(WsFrameServer.java:184)
	at org.apache.tomcat.websocket.server.WsFrameServer.notifyDataAvailable(WsFrameServer.java:164)
	at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.upgradeDispatch(WsHttpUpgradeHandler.java:152)
	at org.apache.coyote.http11.upgrade.UpgradeProcessorInternal.dispatch(UpgradeProcessorInternal.java:60)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:57)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:896)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1744)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)
	at java.base/java.lang.Thread.run(Thread.java:833)

why this happen ? please give some hint

[AlwaysNoobCoder]

@transactional SHOULD ON PUBLIC METHOD ONLY